This invention relates to a cermet composed mainly of titanium carbide, titanium nitride and/or titanium carbonitride, specifically to a high strength nitrogen-containing cermet suitable as the material for cutting tools, such as lathe cutting tools, milling cutter tools, drills, end mills, etc., or the material for wear resistant tools, including slitter, cutting blade and mold tools such as dies for can making, etc., or the material for decorative articles such as watch case, brooch, necktie pin, etc.
Generally speaking, a N (nitrogen)-containing TiC-based cermet with a basic composition of TiC-TiN-Ni tends to be more excellent in strength and plastic deformation resistance as compared with a N-non-containing TiC-based cermet with a basic composition of TiC-Ni. For this reason, the main subject of research and development of TiC-based cermet is becoming in recent years the N-containing TiC-based cermet.
The N-containing TiC-based cermet at the initial stage of development tends to be smaller in N content as 5 to 20% by weight calculated in terms of TiN, but as the effect of containing N becomes evident, it has been investigated to increase the N content, thereby making its effect still greater. As a representative example of the TiC-based cermet with much N content, there is Japanese Patent Publication No. 3017/1988.
Japanese Patent Publication No. 3017/1988 discloses a cermet for cutting tool, having a composition comprising titanium nitride: 25-45% by weight, titanium carbide: 15-35% by weight, tungsten carbide: 10-30% by weight, at least one carbides of Ta, Nb, V and Zr: 5-25% by weight, and Co or Co and Ni (provided that Co&gt;Ni): 7.5-25% by weight, and its hard dispersed phases consisting of the two phases. The one is a NaCl type solid solution phase with the structure comprising titanium carbide as the core and a solid solution of at least one of carbides of Ta, Nb and Zr, tungsten carbide, titanium carbide and titanium nitride surrounding therearound (rim), and the other is a titanium nitride phase, while a binder phase comprises Co, or Co and Ni in which W and Ti exist as solid solution. The cermet disclosed in the published specification, in order to cope with the problem of the TiC-based cermet with much TiN content of the prior art that it has low sinterability and is difficult to obtain high density, provides a readily sinterable and dense cermet by improvement of wettability between the hard dispersed phase and the binder phase by adding no Mo or Mo.sub.2 C. However, since no Mo or Mo.sub.2 C is added, the dispersed phase becomes coarse, and also the particle sizes tend to become non-uniform, whereby there is involved the problem that the advantage of addition of a large amount of TiN to improve strength cannot be fully exhibited.